1. Field of the Invention
The present invention relates to a machine tool with an automatic tool change function, which is capable of making engagement between a key of a tool spindle and a key-way of a tool or a tool holer without stopping rotation of the spindle.
2. Description of the Prior Art
Conventionally, in order to make engagement between a key of a tool spindle and a key-way of a tool, the spindle is stopped at a predetermined angular position.
In order to stop the spindle at such a predetermined angular position, there are required two steps of operations. That is, the spindle is first stopped within a predetermined angular range by controlling a spindle drive motor and then indexed to the predetermined angular position by a mechanical device including, such as, an index plate and an index pin. If the spindle is stopped beyond the predetermined angular range, the spindle drive motor has to be restarted to stop the spindle within the predetermined range. Accordingly, it takes a longer time for stopping the spindle at the predetermined angular position, resulting in a longer tool change time.
Attempt is also made to engage a key of a tool with a key of a tool spindle without stopping rotation of the spindle. However, provision of the key on the tool lacks interchangeability to a standard tool having a key-way, whereby this arrangement is hardly put to practical use.
Furthermore, even if a tool change operation is performed without stopping rotation of the spindle, there is a problem that a large diameter tool with a radially projected cutter has to be returned from the spindle to the tool magazine with its key-way being maintained at a predetermined angular position in order to prevent interference with an adjacent tool in the tool magazine.